<%--
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  User: 刘明福
  Date: 2021/5/30
  Time: 14:12
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--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
这是a页面<br/>
<% //往四个域中都保存了相同的 key 的数据。
    request.setAttribute("key", "request");
    session.setAttribute("key", "session");
    application.setAttribute("key", "application");
    pageContext.setAttribute("key", "pageContext");
%>
pageContext 域是否有值：<%=pageContext.getAttribute("key")%> <br>
request 域是否有值：<%=request.getAttribute("key")%> <br>
session 域是否有值：<%=session.getAttribute("key")%> <br>
application 域是否有值：<%=application.getAttribute("key")%> <br>
</body>
</html>
